Heat Sink Using Latent Heat of LED Street Light

ABSTRACT

There is provided a heat sink using latent heat of an LED street light, wherein a phase change material (PCM) is used in the heat sink to quickly and efficiently dissipate high-temperature heat which generated by LED elements when the street light using LEDs as a light source is turned on. 
     The heat sink using latent heat of an LED street light according to the present invention comprises: a lower plate on which a number of cooling fins protrude at equal intervals and under which an LED module is attached, the LED module having a PCB (printed circuit board) on which a number of LED elements are mounted; an upper plate on which a number of cooling fins protrude at equal intervals, the upper plate to be positioned on the lower plate; and a PCM (phase change material) filled between the upper plate and the lower plated, the PCM absorbing/dissipating thermal energy while changing from liquid to solid or from solid to liquid, wherein the cooling fins protruding on is the upper plate and the lower plate are formed, along a length direction of the heat sink.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-s 2009-66589, filed Jul. 22, 2009, the disclosure of which is hereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat sink using latent heat of an light emitting diode (LED) street light, and more particularly, to a heat sink using latent heat of an LED street light, wherein a phase change material (PCM) is used in the heat sink, to quickly and efficiently dissipate high-temperature heat generated by LED elements when the street light using LEDs as a light source is turned on.

2. Description of the Related Art

Street lights are a lighting system installed along a street, for the traffic safety and security of the street. Many kinds of street lights are installed depending on the installation places, such as highways, city main roads, commercial area roads, residential area roads and parks, among others. High-pressure mercury lamps, fluorescent lamps, sodium lamps and metal halide lamps are used depending on light sources. Since the international trend is toward saving energy, lights used at homes and offices and street lights have been generally replaced with the lights using LEDs which significantly reduce power consumption and maximize illumination effects.

LEDs have high-efficiency of converting electrical power to light. However, since the light emitting regions of LEDs are formed of semiconductor devices, LEDs are relatively weak to heat, compared to the other light emitting elements, such as filaments used in incandescent lights/lamps or cathode rays used in fluorescent lights/lamps. In other words, when LEDs are used for a long time, semiconductor devices are easily degraded by thermal stress caused by heat generated by the light emitting element itself and therefore, LED performance decreases. In this regard, a heat dissipating structure to effectively lose the heat generated by LEDs is very important element in order to allow a large current to flow to LEDs.

Street lights using LEDs have been competitively developed. In these street lights, LEDs are to increasingly output light, to increase the intensity of illumination. Thus, a current is driven at several hundreds mA which is higher than a generally driven current of 20-90 mA in existing LED lights or street lights. In this regard, dissipating heat is raised as a serious issue.

Korean Patent Registration No. 862540 entitled “LED Lamp for Street Light” teaches one of the techniques to effectively dissipate heat generated in a street light using LEDs. The technique taught in the aforementioned document will be briefly described with reference to FIG. 1. A heat sink 1 comprises a first cooling part 2 and a second cooling part 3. The first cooling part 2 has a semi-cylindrical shape and is connected to an LED module. The second cooling part 3 has a cylindrical shape with one end being closed. The closed end of the second cooling part 3 is connected to the first cooling part 2, and the other end of the second cooling part 3 (which is opposite to the closed end) is connected to a socket part. A number of cooling holes 4 to dissipate heat generated by LED elements are formed on a flat surface of the first cooling part 2 connected to the LED module. One end of a spherical part of the semi-cylinder is open and a number of cooling fins are formed inside and outside. Three to five slits are formed lengthwise in the spherical part, to increase the cooling effect. In the second cooling part 3 in the cylindrical shape with the one closed end, a number of cooling fins are formed on the outer circumferential surface of the cylinder.

However, the naturally cooling fins as mentioned above cannot quickly and efficiently dissipate the heat generated by the LED elements. Consequently, the LED elements are degraded, the LED life is shortened, the power consumption increases, and the light emitting efficiency is lowered.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a heat sink using latent heat of an LED street light, wherein the heat sink of the street light using LEDs as a light source is separated into an upper plate and a lower plate, and a phase change material (PCM) is filled between the upper plate and the lower plate, to quickly and efficiently dissipate high-temperature heat generated by from LED elements.

In accordance with an embodiment of the present invention, there is provided a heat sink using latent heat of an LED street light, comprising: a lower plate on which a number of cooling fins are formed so as to protrude at equal intervals and under which an LED module is attached, the LED module having a printed circuit board (PCB) on which a number of LED elements are mounted; an upper plate on which a number of cooling fins are formed so as to protrude at equal intervals, the upper plate to be positioned on the lower plate; and a phase change material (PCM) filled between the upper plate and the lower plate, the PCM absorbing or dissipating thermal energy while changing from liquid to solid or from solid to liquid, wherein the cooling fins formed so as to protrude on the upper plate and the lower plate are formed in a length direction of the heat sink.

Preferably, the position of each of the protruding cooling fins on the upper plate is arranged between the positions of the two adjacent protruding cooling fins on the lower plate.

Preferably, the cross section of the heat sink is flat or has a

shape in which a middle part is higher than both end parts in a width direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail a preferred embodiment thereof with reference to the attached drawings in which:

FIG. 1 illustrates a conventional heat sink of an LED street light;

FIG. 2 is a perspective view of a heat sink of an LED street light according to the present invention;

FIG. 3 is a sectional view of the heat sink of FIG. 2 being separated; and

FIG. 4 is a sectional view of the heat sink being connected.

FIG. 5 is a perspective view and sectional view of the heat sink of another embodiment of an LED street light according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the invention is shown so that those of ordinary skill in the art can easily carry out the present invention.

A heat sink 10 using latent heat of an LED street light according to the present invention will be described with reference to FIGS. 2 through 5. The most significant characteristic of the heat sink 10 is that the constituents are separated. That is, the heat sink 10 comprises: a lower plate 11, an upper plate 12 and a phase change material (PCM) 13 filled between the lower plate 11 and the upper plate 12.

On the lower plate 11, a number of cooling fins 14 are formed to protrude in an elongated manner, along a length direction of the heat sink 10. Under the lower plate 11, an LED module 20 is attached. The LED module 20 has a printed circuit board (PCB) 21 on which a number of LED elements 22 are mounted. The cooling fins 14 formed on the lower plate 11 absorb heat generated in the LED module 20 and function as a container to hold the PCM 13 filling the space between the cooling fins 14. That is, in the cooling fins 14 protruding in a number of rows, each space between the adjacent cooling fins 14 functions as the container to prevent the filled PCM 13 from moving to any one side.

The upper plate 12 is positioned on the lower plate 11. On the upper plate 12, a number of cooling fins 14′ are formed to protrude in an elongated manner, along the length direction of the heat sink 10. The cooling fins 14′ broaden the surface area of the upper plate 12, to broaden the heat dissipation area.

The position of each of the protruding cooling fins 14′ in a number of rows on the upper plate 12 is arranged between the positions of the two adjacent protruding cooling fins 14 on the lower plate 11. Preferably, each of the cooling fins 14′ may protrude at a middle position of each of the PCM 13 filled in the space between the two adjacent cooling fins 14 on the lower plate 11, so that the cooling fins 14′ can quickly absorb the heat from the PCM 13.

The PCM 13 is filled between the lower plate 11 and the upper plate 12. The PCM can be called a ‘latent heat storage material’. The PCM is in a liquid state when it absorbs heat, and it is in a solid state when it is cooled. As the PCM absorbs and dissipates heat within any required temperature range, it changes from solid to liquid or from liquid to solid, thereby absorbing/dissipating thermal energy.

In the heat sink 10 as structured above, the heat generated by the LED elements 22 is firstly absorbed through the lower plate 11. After the PCM 13 absorbs the heat absorbed in the lower plate 11, the upper plate 12 absorbs the heat from the PCM 13 and dissipates the heat outside. Therefore, the heat is quickly and efficiently dissipated. The amount of the PCM 13 varies depending on the number of the LED elements. However, about 1.6˜1.8 kg PCMs are filled for a general street light, to maintain the temperature of the LED elements 22 generating heat at 60° C. or below and to maintain the high light efficiency and long life span of the LED elements 22.

The heat sink 10 may vary depending on the shape of the LED module 20 used for the street light. However, preferably, the cross section of the heat sink 10 may be in a

shape in which a middle part is higher than both end parts in a width direction of the heat sink 10. The cross section of the heat sink 10 may be in a flat shape even though it is not illustrated in the attached drawings.

The materials of the upper plate 12 and the lower plate 11 of the heat sink 10 use metals having high heat conductivity. Taking the heat conductivity characteristic and cost into consideration, it is most preferable to use aluminum based metals.

As described above, in the heat sink using latent heat of the LED street light according to the present invention, the heat sink of the street light using LEDs as the light source is separated into the upper plate and the lower plate, and the PCM is filled between the upper plate and the lower plate. Therefore, when heat generated in the LED module is firstly dissipated through the lower plate, the PCM being in the cool solid state quickly absorbs the heat dissipated through the lower plate and changes to liquid. Then, the absorbed heat is quickly transferred to the upper state, to be secondly dissipated on the upper plate outwardly. Thus, since high-temperature heat generated by the LED elements is quickly and efficiently dissipated, the LED elements are continuously maintained so as not to reach a predetermined high temperature, thereby maintaining the high light efficiency and long life span of the LED elements.

The invention has been described using a preferred exemplary embodiment. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiment. On the contrary, the scope of the invention is intended to include various modifications and alternative arrangements within the capabilities of persons skilled in the art using presently known or future technologies and equivalents. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

BRIEF DESCRIPTION OF REFERENCE NUMBERS OF MAJOR ELEMENTS

10: heat sink 11: lower plate 12: upper plate 13: phase change material (PCM) 14, 14′: cooling fins 20: LED module 21: PCB 22: LED elements 

1. A heat sink using latent heat of an LED street light, comprising: a lower plate on which a number of cooling fins protrude at equal intervals and under which an LED module is attached, the LED module having a PCB (printed circuit board) on which a number of LED elements are mounted; an upper plate on which a number of cooling fins protrude at equal intervals, the upper plate to be positioned on the lower plate; and a PCM (phase change material) filled between the upper plate and the lower plated, the PCM absorbing/dissipating thermal energy while changing from liquid to solid or from solid to liquid, wherein the cooling fins protruding on the upper plate and the lower plate are formed, along a length direction of the heat sink.
 2. The heat sink according to claim 1, wherein the position of each of the protruding cooling fins on the upper plate is arranged between the positions of the two adjacent protruding cooling fins on the lower plated.
 3. The heat sink according to claim 1, wherein the cross section of the heat sink is flat.
 4. The heat sink according to claim 1, wherein the cross section of the heat sink is in a

shape in which a middle part is higher than both ends in a width direction of the heat sink.
 5. The heat sink according to claim 1, wherein the material of the upper plate and the lower plate of the heat sink is aluminum. 